1. Field of the Invention
The present invention relates to a method of measuring electric charge of a semi-conductor wafer, and more specifically to measurement of electric charges accumulated in an insulating film of a semiconductor wafer.
2. Description of the Related Art
Semiconductor wafers are exposed to charged particles in ion implantation processes, plasma CVD (Chemical Vapor Deposition) processes, and other plasma- related processes for etching and resist removal. These processes accumulate electric charges proximate the surface of a semiconductor wafer, or more specifically inside an insulating film of the semiconductor wafer. In a rinsing process, friction between the semiconductor wafer and gaseous or liquid rinse substance electrically charges surface layers of the semiconductor wafer.
Accumulation of excessive electric charges in the surface layers of a semiconductor wafer makes a high electric field, which destroys the structure of semiconductor devices to deteriorate properties thereof, thus lowering the yield of manufacture of semiconductors. The amount of the electric charge accumulated in the surface layers of a semiconductor wafer, however, depends highly on the individual processing apparatus even for the same process; well-adjusted processing apparatus will produce a smaller charge whereas poorly-adjusted apparatus will produce a greater charge. Measurement of the electric charges in the surface layers of a semiconductor wafer is thereby useful for evaluating the conditions of each processing apparatus.
Conventionally, the electric charge is measured by: bringing a specific probe into contact with or proximate to a target semiconductor wafer; measuring a potential on the surface of the target semiconductor wafer; and determining the accumulated charges based on the surface potential.
The surface potential, however, only indicates a rough magnitude of the electric charges, and the amount of the electric charges cannot be obtained from measurement. In other words, there is no conventional method and apparatus for measuring the amount of electric charge in a surface layer of a semiconductor wafer.